In-line filter probe for process analysis

ABSTRACT

An in-line filter probe for process analysis. The probe, which has a U-shaped porous tube mounted on a support and sealed at the tube&#39;s midsection, is placed in a process stream to provide filtered samples of the stream.

BACKGROUND OF INVENTION

The present invention relates to process analysis. More particularly,the invention relates to a sampling system for process analysisutilizing an in-line filter probe.

Sample cleanup for process analytical chemistry of liquid samples almostinvariably involves a filtration step. Accomplishing such filtration isdifficult, due to the need for extreme long-term reliability withminimal maintenance requirements.

The present invention provides a sampling system and correspondingmethodology which accomplishes the task of sample filtration, protectsthe elements of the cleanup transport system, removes the absoluteminimum amount of sample from the process, and provides the capabilityof automatically cleaning the filtration elements, thereby greatlyreducing and possibly eliminating the need for manual cleaning andreplacement of the filter elements.

SUMMARY OF INVENTION

In general, the present invention in a first aspect provides a samplingsystem for process analysis utilizing an in-line filter probe. Thesystem comprises (a) a support element; (b) a first segment of poroustubing having an open first end and a closed second end, mounted on thesupport element; and (c) a second segment of porous tubing having anopen first end and a closed second end, mounted on the support element.

In a second aspect the invention provides a method for fabricating anin-line filter probe. The method comprises (a) providing a supportelement; (b) mounting on the support element in a U-shaped configurationa porous tube open at first and second ends; and (c) sealing the tubebetween its first and second ends, thereby forming first and secondopen-ended segments connected to one another by a sealed third segment.

In a third aspect the invention provides a method for obtaining samplesfor process analysis utilizing an in-line filter probe. The methodcomprises (a) providing an in-line filter probe comprising a supportelement, a first segment of porous tubing having an open first end and aclosed second end, mounted on the support element, and a second segmentof porous tubing having an open first end and a closed second end,mounted on the support element; (b) disposing the filter probe in afluid to be sampled; and (c) circulating the fluid through the poroustube.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1-A is a top view of an in-line filter probe made in accordancewith the principles of the present invention.

FIG. 1-B is a side view of the in-line filter probe shown in FIG. 1-A.

FIGS. 2-A and 2-B are schematic representations of a first embodiment ofa sampling system utilizing the in-line filter probe shown in FIGS. 1-Aand 1-B, made in accordance with the principles of the presentinvention.

FIG. 3 is a schematic representation of a second embodiment of asampling system utilizing the in-line filter probe shown in FIGS. 1-Aand 1-B, made in accordance with the principles of the presentinvention.

FIG. 4 is a schematic representation of a third embodiment of a samplingsystem utilizing the in-line filter probe shown in FIGS. 1-A and 1-B,made in accordance with the principles of the present invention.

FIG. 5 is a schematic representation of a fourth embodiment of asampling system utilizing the in-line filter probe shown in FIGS. 1-Aand 1-B, made in accordance with the principles of the presentinvention.

FIG. 6 is a schematic representation of a fifth embodiment of a samplingsystem utilizing the in-line filter probe shown in FIGS. 1-A and 1-B,made in accordance with the principles of the present invention.

FIG. 7 is a schematic representation of a sampling system comprising thein-line filter probe disposed in a flow cell, in accordance with theprinciples of the present invention.

FIG. 8 is a schematic representation of a sampling system comprising thein-line filter probe installed in a containment vessel, in accordancewith the principles of the present invention.

DETAILED DESCRIPTION

More specifically, reference is made to FIGS. 1-A and 1-B, in which isshown an in-line filter probe, made in accordance with the principles ofthe present invention, and generally designated by the numeral 2. Thein-line filter probe 2 comprises a support element 2 a on which ismounted a U-shaped porous tube 2 b. The tube 2 b is preferably a singlelength of porous poly(tetrafluoroethylene) tubing having a porosity ofabout ten microns. The porosity or material of the tube 2 b, however,may be changed as required or desired.

The filter tube 2 b is anchored at its first and second open ends 2 cand 2 d by termination assembles 2 e which form a leak-tight andphysically strong grip on the ends 2 c and 2 d of the tube 2 b whenconnected thereto by ferrules 2 f and threaded ports 2 g. The filtertube 2 b is securely attached to the support element 2 a by end cap 2 i.The termination assemblies 2 e are constructed and arranged to allowconnection of transport tubing and fittings (not shown) to the ends 2 cand 2 d of the filter tube 2 b.

After mounting, the end cap 2 i is screwed into place to compress asegment 2 j of the filter tube 2 b, pinching it shut and isolating firstand second separate filtration segments 2 k and 2 l. It is possible touse two separate filter tubes and/or other geometries of dual-elementfiltration devices to accomplish the objectives and carry out thefunctions disclosed herein, but the geometry shown in FIGS. 1-A and 1-Bprovides the most compact configuration possible, and is the preferredembodiment.

Reference is now made to FIGS. 2-A and 2-B, in which is shown a firstembodiment of a sampling system utilizing the in-line filter probe 2,made in accordance with the principles of the present invention andgenerally designated by the numeral 4.

The filter probe 2 is installed as part of the sampling system 4, whichadds to the filter probe 2 a stream-switching valve 6 and a samplecirculation pump 8. The stream-switching valve 6may be a single four orsix-port valve plumbed up in a stream-switching configuration, ormultiple three-way valves to perform the same function. A singlefour/six-port valve simplifies the necessary control-switching hardware(not shown). The circulation pump 8 may be of any type such ascentrifugal, gear, or piston that provides the necessary motive force todrive sample fluid 70 through the sampling system 4, the direction offlow of the fluid 10 being indicated by arrows.

Referring now to FIG. 2-A, under process pressure and suction from thepump 8, process fluid 10 enters the first filtration segment 2 k of thein-line filter probe 2. The fluid 10 then circulates through thestream-switching valve 6 and circulation pump 8, and under pressure fromthe pump 8 is forced back to and through the second filtration segment 2l. Particulate matter is removed from the circulating stream 10 by thefirst filtration segment 2 k, so that the stream-switching valve 6 andpump 8 are exposed only to particle-free fluid, thereby minimizing wearand extending the operational life of the valve 6 and pump 8.

At some experimentally-determined optimum time, or by means of atriggering signal derived from pressure and/or flow sensors (not shown),the stream-switching valve 6 is automatically actuated. As shown in FIG.2-B, the flow-path geometry of the fluid 10 is such that upon saidactuation the direction of flow through the first and second filtrationsegments 2 k and 2 l is reversed, but the direction of flow through thepump 8 and valve 6 remains unidirectional. After flow reversal, thesecond filtration segment 2 l becomes the inlet filtration segment, andthe first filtration segment 2 k the outlet filtration segment. Anyparticulate matter which has built up as a filter cake upon or depositedwithin the pores of the first filtration segment 2 k is now flushed outby clear sample fluid 10 flowing in the reverse direction through thefiltration segment 2 k.

Reference is now made to FIG. 3, in which is shown a second embodimentof a sampling system utilizing the in-line filter probe 2, made inaccordance with the principles of the present invention and generallydesignated by the numeral 12. The configuration shown in FIG. 3discloses the application of the in-line filter probe 2 to analyticalinstrumentation such as a gas chromatograph, a high-pressure liquidchromatograph, a flow-injection analyzer, or other analyticalinstruments, utilizing injection valves for sample introduction.

The sampling system 12 comprises the filter probe 2, stream-switchingvalve 6, circulation pump 8, block valves 14, a three-way ball valve 16,a pressure gauge 18, and an injection valve 20 which introduces anintermittent sample to a flow-injection analyzer 20 a.

The block valves 14, which are preferably operated manually, aredisposed between and connect the stream-switching valve 6and the poroustubing 2 k, 2 l to one another. The three-way block valve 16, disposedbetween and connecting the injection valve 20 and the flow-switchingvalve 6to one another, provides means for a manual chemical or solventbackwash.

Reference is now made to FIG. 4, in which is shown a third embodiment ofa sampling system utilizing the in-line filter probe 2, made inaccordance with the principles of the present invention and generallydesignated by the numeral 22. The configuration shown in FIG. 4 providesa second example of the application of the in-line filter probe 2 toanalytical instrumentation. The sampling system 22 is identical to thesampling system 72 shown in FIG. 3, except that a sequential-injectionanalyzer 24 is utilized instead of the flow-injection analyzer 20 a, andthe means of sample takeoff are modified accordingly.

In this application, the necessary sample volume is extracted undersuction by means of a downstream syringe pump and sequential-injectionanalyzer stream-selection valve. This application is particularlyadvantageous, as it adds the capability to automatically backwash theporous filter segments in addition to the normal manual backwash. Thechemical backwash is accomplished by devoting one reagent channel of thesequential-injection analyzer (SIA) stream-selection valve 24 a to thedesired backwash chemical. Other channels connect to a carrier-solventreservoir 25 and a detector 27. In addition, the SIA selection valve 24a is switched so that the SIA syringe pump 24 b and holding coil 24 careconnected to a backwash reagent reservoir 24 d. Under suction of thesyringe pump 24 b, an aliquot/aliquant of the backwash reagent 24 e ispulled through the selection valve 24 a into the SIA holding coil 24 c.The SIA stream-selection valve 24 a is then actuated so that the syringepump 24 b and holding coil 24 care placed in fluid communication withthe SIA selection-valve 24 a port communicating with the in-line filterprobe 2 and pump 8. This port is the same as that normally used forsample takeoff under syringe-pump action. Under syringe-pump pressure,the aliquot/aliquant of backwash reagent is pushed until it enters theunidirectional pumped flow path of the in-line filter probe 2. Then,under pressure from the sample circulation pump 8, the backwash chemicalis pushed to and through the return porous filter segment 2 k or 2 l. Asthe chemical passes through the pores of the porous tubing 2 k or 2 l,the backwash chemical reagent dissolves and removes any wash-resistantparticulate matter which might irreversibly block the pores, and whichcannot be removed by a physical backwash. The chemical backwash justdescribed is repeated after the stream-switching valve 6 has reversedthe direction of fluid 10 flow, thereby chemically backwashing bothfiltration segments 2 k and 2 l. These chemical backwashes can becarried out under automatic computer control as frequently and as oftenas desired to obtain the desired or required degree of filter cleanup.

Reference is now made to FIG. 5, in which is shown a fourth embodimentof a sampling system utilizing the in-line filter probe 2, made inaccordance with the principles of the present invention and generallydesignated by the numeral 26. The sampling system 26 illustrates a thirdexample of the use of the in-line filter probe 2 in combination with ananalytical instrument; in this case, a spectrometer flow cell 28. Asshown in FIG. 5, the spectrometer flow cell 28 is simply inserted intothe unidirectional flow path of the filter probe 2, the only requirementbeing that the flow cell 28 be of sufficiently small internal volume asnot to introduce significant washout lag time into the analytical cycle.If chemical backwash is desired, a dedicated syringe pump can be added.The inlet point for such a backwash capability would be downstream ofthe flow cell 28. The same considerations would apply to the samplingsystem 12 shown in FIG. 3, or to a similar system using a gaschromatograph (not shown) as the analytical instrument.

Reference is now made to FIG. 6, which illustrates such a dedicatedchemical backwash system, generally designated by the numeral 30. Thesystem 30 comprises a container 32 of backwash reagent and a dedicatedsyringe pump 34.

All of the chemical/solvent cleaning means thus far described areintermittent in nature. For really difficult streams, it is possible toarrange for continuous chemical/solvent cleaning action in addition tocontinuous physical backwashing. In this arrangement a separatecontinuous pump replaces the syringe pump shown in FIG. 6, and thecleaning chemical is continuously pumped into the unidirectional flowloop.

It is important to note that the above means of physical and chemical donot require any interruption of clean sample flow to the analyticalfinish at any time (with the exception of the SIA application, wheresuch stoppage of flow is inherent in sample extraction). Even in thatcase, however, flow continues uninterrupted through the sample bypass,so fresh sample is always available.

In addition to the advanced sample cleanup and filter-treatmentcapabilities provided by the present invention, the filter probe 2provides the unique capability of being usable either in a flow cellremote from the sample point or inserted directly in a process vessel orpiping.

Reference is now made to FIG. 7, in which is shown a sampling systemutilizing the filter probe 2 disposed in a process flow cell 35, thesampling system being generally designated by the numeral 36. The filterprobe 2 is small enough to fit easily inside one-inch pipe or tubing 38,thereby permitting the filter probe 2 to fit easily into a flow cell 35constructed of one-inch tube fittings (Swagelok® style). The flow cell35 is typically mounted at the analyzer house, and raw sample circulatedto and through the flow cell 35 by process pressure or a dedicated pump.

Reference is now made to FIG. 8, in which is shown the filter probe 2installed in pipe or vessel 42, the sampling system being generallydesignated by the numeral 40. Since the connector ends of the in-linefilter probe 2 are designed to socket into a one-inch tube size(Swagelok® type) fitting, the probe 2 can be installed in such aone-inch union at the end of a long length 44 of one-inch tubing. Thislong length 44 of one-inch tubing can be further placed in a lockchamber 46 arrangement that will allow easy insertion into and removalfrom large-diameter process piping 42, without need to shut process flowoff for such insertion or removal.

Such a probe configuration can be inserted directly into tanks 42 andother such vessels. All that is required is a sufficient length ofone-inch tube/pipe and interconnecting tubing from the two filterelements to the filter probe's 2 switching valve and circulating pump.In such installations it is envisioned that the backwash valve andcirculating pump would be mounted as close to the tank/pipe aspracticable, with the unidirectional-flow portion of the probe's 2circulation loop flowing to the location of the analytical finish.

In summary, the in-line filter probe 2 assembly provides maximallyreliable sampling for automated process analysis. It consumes/removesand treats the absolute minimum sample required for analysis, in mostcases removing only a few microliters per analytical cycle, and in somespecial cases removing no material permanently from the process. Thefilter probe 2 is especially suitable for small-volume reactors. Itprovides the capability to both physically and chemically automaticallyremove filter-plugging materials from the probe 2. The compact size andunitary construction of the probe 2 facilitate ease of insertion intoand removal from the process for any additional maintenance and/orreplacement. It provides means of continuously physically back flushingthe filter element using filtered sample solution while simultaneouslyproviding filtered sample. Prior-art filters tangentially flush, usingunfiltered sample solution, and thus do not address completely theproblem of blocked pores. Some systems periodically blow back todislodge cake, using either the sample or even compressed air, but nosampling can take place while this is in progress. It provides a meansof introducing an additional intermittent or even continuouschemical/solvent wash solution. Because the system provides a means ofsimultaneous back flushing and filtration, washing and filtering can bedone concurrently and continuously (or-intermittently) withoutinterrupting the flow of filtered sample. It can be madeself-maintaining by using pressure or flow set points to trigger theswitching valve, operated on a time-based control scheme or controlledby either an instrument or a plant computer.

I claim:
 1. A sampling system for process analysis utilizing an in-linefilter probe, the system comprising: (a) a support element; and (b) aU-shaped porous tube mounted on the support element, the U-shaped poroustube comprising a first segment having an open first end and a closedsecond end, and a second segment having an open first end and a closedsecond end, the second ends of the first and second segments beingclosed and connected to one another by a sealed third segment.
 2. Thesampling system of claim 1, wherein the third segment of the porous tubeis sealed by compression.
 3. A method for obtaining samples for processanalysis utilizing an in-line filter probe, the method comprising thesteps of: (a) providing an in-line filter probe comprising a supportelement and a U-shaped porous tube mounted on the support element, theU-shaped porous tube comprising a first segment having an open first endand a closed second end, and a second segment having an open first endand a closed second end, the second ends of the first and secondsegments being closed and connected to one another by a sealed thirdsegment; (b) disposing the filter probe in a fluid to be sampled; and(c) circulating the fluid through the porous tube.
 4. The method ofclaim 3, wherein the third segment of the porous tube is sealed bycompression.